A sensitive method for measuring in vivo permeability of surface enamel will be applied to the maxillary incisors of two groups of children (N greater than or equal to 30) aged 7 to 8 years and 14 to 15 years in order to study possible changes in permeability related to maturation of the teeth. The same method will be used to assess the in vivo demineralization of enamel produced by acids of similar strength as that of citrous fruits or soft drinks, and to monitor subsequent remineralization. Procedures for evaluating in vivo effects on remineralization of fluoride and other agents will be developed. In addition, the protein extracted from the enamel during the period of demineralization and the extractable protein deposited during remineralization will be subjected to amino acid analysis. With the purpose of developing an intraoral cariogenicity test for foodstuffs, the permeability test will also be used to detect the early stage of caries produced in enamel blocks mounted in a full set of dentures.